Copolycarbonates which contain as part of their molecular structure, derivatives of sulfonyl diphenyl have been recognized by the art to offer advantages in terms of flame resistance, good stress cracking characteristics, high service temperature and mechanical properties.
U.S. Pat. No. 3,269,986 discloses polycarbonate resins based on dihydroxy polysulfones prepared by transesterification or by polymerization in a homogeneous phase. U.S. Pat. No. 3,271,367 discloses the preparation of polycarbonates of dihydroxydiarylene sulfones. A two-phase interfacial polycondensation process is referred to and a preparation of copolycarbonates containing over 30 percent by weight of 4,4'-dihydroxydiphenyl sulfone is reported in Example 5. It is noted however that the example entailed the old "dough " batch process in which the viscous mass of polycarbonate and organic solvents are washed free of impurities in a kneader.
A batch reaction for the preparation of polycarbonates generally is one where all the reactants, except the carbonate precursor, i.e. phosgene, are first charged to the reactor and the carbonate precursor is then metered into the reaction mixture over a predetermined time. A drawback of this reaction is a localized imbalance of reactants which causes considerable side reactions to take place resulting in an inferior polycarbonate product.
In contrast, in the continuous reaction the reactants are metered in stoichiometric amounts, except for a slight excess of phosgene, into a mixing chamber (precondensation in a reactor cooler or primary reactor). This reaction results in a relatively low molecular weight product which contains chlorocarbonic end groups. Proceeding to the secondary condensation reaction where additional catalyst is introduced, the end groups hydrolyze and in the presence of additional base further react to build up the high molecular weight product.
In addition to the improvement in product quality, the continuous process is considerably more economical than the batch process.
U.S. Pat. No. 3,419,526 discloses the preparation of a copolycarbonate of 4,4'-bis[(4-hydroxy)phenoxy]-phenyl-sulfone in an interfacial process using triethylamine as catalyst. Films of a copolycarbonate of 75 percent by weight 4,4'-dihydroxyphenyl sulfone and 25 percent by weight of bisphenol-A were prepared in a homogeneous medium in accordance with Example I, part B of U.S. Pat. No. 3,737,409. Flame resistant copolycarbonate resins entailing structural units derived from 4,4'-dihydroxydiphenyl sulfone were disclosed in U.S. Pat. No. 3,912,688. Among the suitable catalysts in the phase-interface condensation process for the preparation of the copolycarbonates of that invention there are listed quaternary ammonium salts. Phase transfer catalysis for two-phase reactions including the interfacial polycondensation of polycarbonates has been reported. See Interfacial Synthesis, Vol. III, Recent Advances, Carraher, C. E. and Preston, J., editors, Marcel Dekker Inc., New York, and Phase Transfer Catalysis, Principles and Techniques, Starks, C. M. and Liotta, C. Schnell et al reported the use of tertiary amines or quaternary ammonium compounds for accelerating and improving the synthesis of polycarbonates--see for instance H. Schnell, "Chemistry and Physics of Polycarbonates", Interscience Publishers, New York, 1964. A bifurcated process for the preparation of copolycarbonates including substantial amounts of 4,4'-dihydroxydiphenyl sulfone is described in U.S. Pat. No. 4,404,351.
Copolycarbonates containing low levels of dihydroxydisulfone, i.e. less than 15 wt. %, may be prepared using interfacial reaction techniques. The incorporation of higher amounts however is known to cause loss of reaction control because unworkable emulsions are formed.